DevelopmentsinEarthSurfaceProcesses ...

Climate and Geomorphologic-related Disasters in Latin America 7
of Panama and north Colombia. Along the Atlantic coast the trough migrates only a
few degrees of latitude with the seasonal cycle.
In austral winter, the subtropical high-pressure centers present near 30°S in the
Pacific Ocean and at 27°S over the Atlantic Ocean are connected across the South
American continent. During the austral summer, the belt of high pressure in the
subtropics is interrupted by heating of the landmass, generating lower pressure over
land that divides the semipermanent subtropical anticyclones.
Thanks to the characteristic cloud cover, the ITCZ is easy to identify in the
rainfall patterns shown in Figure 1.4. It crosses the western coast of Colombia at
approximately 5°N, and curves around the Amazon Basin east of the Andes
Mountain Range, reaching as far as the northern part of Paraguay. It curves
northeastward over the eastern part of the Amazon Basin and extends into the
Atlantic Ocean near 5°N.
Northeast trade winds prevail to the north of the ITCZ (Fig. 1.4), blowing with
moderate intensity on the northern coast of the continent between the Amazonas
and Panama. To the south of the ITCZ, along the oriental coast extending to
15.5°S, the trade winds blow from the southeast in the oceanic areas and swing
gradually to the east and northeast as they penetrate inland. Further south, toward
the Drake Strait, midlatitude westerly winds are intense and persistent.
During the austral winter, the location of the ITCZ coincides with the warmest
SSTs and reaches its northernmost position (Fig. 1.4b). Northeast winds are felt
only over the Caribbean coasts of Venezuela and Colombia. The southeast trade
winds are located on the southern side of the ITCZ, over the Atlantic between 5°N
and 15°S. Once again during this season, midlatitude westerly winds are intense and
persistent near the Drake Strait. The wind systems are subject to strong local
influences, particularly due those of topography in mountainous regions.
2.4. Rainfall Patterns
The wind, pressure, and temperature patterns described in the previous sections
give rise to the observed seasonal variability of precipitation in the Americas.
This complex seasonal cycle is strongly influenced by the surrounding oceans,
topography, land surface type, thermodynamic conditions, and large-scale circulations.
Together, the seasonal cycle of winds, precipitation, temperature, and
sea-level pressure fields in tropical South, Central, and North America share
general characteristics with classical monsoon climates in other parts of the world
(Zhou et al. 1988) and can therefore be referred to as the American Monsoon
System.
2.4.1. The South American Monsoon System
Figure 1.4 shows the climatological low-level winds and the Global Precipitation
Climatology Project (GPCP) precipitation patterns in South America during the
austral and boreal summers. The peak rainy season in South America occurs during
December through February (Fig. 1.4a) and is referred to as the South American
Monsoon System (SAMS). The SAMS is characterized by a precipitation pattern that